A number of pathophysiological observations in humans and animal models led to the hypothesis that atherosclerosis, a disease of the large arteries that is the primary cause of coronary heart disease (CHD) and stroke, is a multifactorial chronic inflammatory disease in which low plasma levels of HDL and high plasma levels of LDL, are a strong predictor of the condition. LDL oxidation is considered to be an essential process in the development of atherosclerotic lesions. The pro-inflammatory constituents of oxidized LDL are various oxidized phospholipids resulting from the scission and rearrangement of oxidized, unsaturated fatty acids. HDL and HDL-associated enzymes possess anti-atherogenic properties that are due, in part, to their inactivation of oxidized LDL. Although genetic and biochemical studies demonstrated anti-atherogenic role for paraoxanase-1 (PON1), a HDL associated protein, to date, the physiological functions of PON family of proteins; PON1, PON2 and PON3, remain unknown. Based on our preliminary findings, we hypothesize that PON2 and PON3 proteins inhibit the accumulation of oxidized phospholipids in LDL, protect artery wall cells against oxidative stress from reactive oxygen species (ROS) and oxidized phospholipids, and prevent the development of atherosclerotic lesions. In this application, we propose to i) characterize the biochemical and enzymatic properties of PON2 and PON3 proteins, ii) determine cellular localization, products of enzyme activity and the expression levels of PON2 and PON3 proteins in HDL and hyperchloesterolemic animal models, iii) develop transgenic mice and knockout mice to determine the physiological function of PON2 and PON3 proteins as well as the role of PON2 and PON3 in atherosclerosis, and iv) identify and characterize proteins that interact with PON2 and PON3 to delineate the biological substrates of PON2 and PON3 proteins. Understanding the biology and function of the PON proteins will pave way for the discovery of novel therapeutic agents in the fight against atherosclerosis and other inflammatory diseases.